This invention relates to a radiation detection device for detecting ionizing beam discharges such as gamma rays, x-rays, electron beams, charged particle beams and neutral particle beams. Specifically, it relates to a radiation detection device which can measure radiation beams which exist for a very short time (of the order of subnanoseconds or less) from the appearance of photoemission to extinction.
To detect or measure ionizing beams, a scintillation counter is used. In recent years, it has become necessary to measure very short pulse radiations of the order of nanoseconds in a radiation field.
The scintillator must have the following functions: (i) High scintillation efficiency and large photoemission amount (ii) Short photoemission appearance time and decay time (iii) High resistance to radiation (iv) It should permit measurement of the radiation amount. Until now, however, no scintillator material was capable of satisfying all these conditions simultaneously.
In the scintillators of the prior art, inorganic crystals such as NaI (Tl), CsI (Tl) and ZnS (Ag) were used, but they could only be used in units as slow as microseconds (10xe2x88x926) from the appearance of photoemission to extinction, and were not able to respond to the measurement of short pulse radiations of nanosecond order (10xe2x88x929). On the other hand, although organic crystals such as anthracene or naphthalene had a fast response in nanosecond units, their fluorescence efficiency was low and photoemission amount was small, hence measurement precision was low and as their radiation resistance was low, they were not suitable for practical use.
For this purpose, the structure and characteristics of organic-inorganic laminar perovskites, especially bis(alkylammonium) metal (II) tetrahalides represented by (CnH2n+1NH3)2MX4 (in the formula, n is an integer from 2-18, M is Cd, Cu, Fe. Mn, Pd or Pb, X is Cl, Br or I), have been studied (E. D. T. Ogawa and Y. Kanemitsu, xe2x80x9cOptical properties of low-dimensional Materialsxe2x80x9d, Chapter 6, World Scientific (1995); D. B. Mitzi, xe2x80x9cTemplating and structural engineering in organic-inorganic perovskitesxe2x80x9d, J. Chem. Soc., Dalton Trans., 2001, 1-12). The structure of organic-inorganic laminar perovskites represented by (CnH2n+1NH3)2PbI4 (in the formula, n is 4-14) have been studied in particular detail.
It is known that due to the low-dimensional (two-dimensional in FIG. 1) quantum well structure shown in FIG. 1, they have a stable and powerful exciton emission (T. Ishihara et. al. Solid State Communications 69(9), 933-936 (1989)), and very interesting results have been obtained such as photoemission in the visible region due to electronic transitions in the PbI4 layer which is the inorganic layer, when irradiated with ultraviolet light.
Problems to be Solved by the Invention
The inventors discovered that the radiation resistance of exciton photoemissions of perovskite organic-inorganic hybrid compounds having a quantum well structure was high, and that this type of perovskite organic-inorganic hybrid compound could be used for detecting very short pulse ionizing beams and measuring radiations. This invention thus provides a new scintillator using exciton emissions, and makes it possible to provide a simple device which can, in a short time, detect very short pulse radiations which formerly required very complex systems and difficult procedures.
Regarding the decay constants of the emissions of these scintillators, whereas that of anthracene which is a typical organic crystal is 30 nanoseconds, and that of sodium iodide which is a typical inorganic crystal doped with thallium is 230 nanoseconds, it is reported that the free exciton emission of halide organic-inorganic perovskite compounds is 91 picoseconds, which is at least two digits faster response than that of the organic crystal.
Means to Solve the Problems
This invention provides a radiation detection device which, due to the low dimensional quantum well structure of perovskite organic-inorganic hybrid compounds, can detect very short pulse ionizing beams (gamma rays, x-rays, electron beams, charged particle beams and neutron beams) which was not possible using radiation detection devices applying the scintillators of the prior art. This is done by using intense exciton emissions which exist for only a short time from appearance to extinction, and also permits the radiation characteristics to be measured.
This invention focuses on the fact that exciton emissions of perovskite organic-inorganic hybrid compounds are short-lived and powerful, and that this exciton emission can be used for radiation detection and radiation amount measurement. Pigments, which are well known as exciton emission materials, have a low radiation resistance, and therefore exciton emission materials could not be used as scintillators in the prior art. However, the inventors systematically studied the strong irradiation of perovskite organic-inorganic hybrid compounds having the structures shown in FIG. 1 and FIG. 2, and the exciton emissions of these compounds, and discovered that these compounds had a very high radiation resistance. The life of exciton emissions of the perovskite organic-inorganic hybrid compounds of this invention was a short as several tens of picoseconds, the flux energy of the excitons reached 300 meV or more, and they had a strong exciton emission even at room temperature.
Therefore, the perovskite organic-inorganic hybrid compounds of this invention having a high radiation resistance can be used as ideal exciton emission scintillators satisfying all the conditions (i)-(iv) which were desired in the prior art.
Specifically, this Invention Provides
A radiation detection device using a perovskite organic-inorganic hybrid compound as a scintillator, the formula of said compound being (R1xe2x80x94NR113)2MX4 or (R2xe2x95x90NR122)2MX4, or alternatively, (NR133xe2x80x94R3xe2x80x94NR133)MX4 or (NR142xe2x95x90R4xe2x95x90NR142)MX4 (in the formula, R1 is a monovalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R2 is a divalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, and may be cyclic, R3 is a divalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R4 is a tetravalent hydrocarbon group which may contain a heterocyclic ring and may be substituted by halogen atoms, R11-R14 are, identical or different, hydrogen atoms or alkyl groups having less than two carbon atoms, M is a Group IVa metal, Eu, Cd, Cu, Fe, Mn or Pd, and X is a halogen atom). This radiation detection device can measure the radiation amount of the detected radiation. Further, this radiation detection device may comprise scintillators disposed on a solid substrate. Any suitable solid substrate can be used, provided it has no photoemission and does not interfere with the measurement, and it may for example be a silicon crystal. Further, the hydrocarbon groups in the above perovskite organic-inorganic hybrid compound may be cross-linked. This invention may be used as a radiation scintillator of the above perovskite organic-inorganic hybrid compound.